1. Field of the Invention
The present invention relates generally to X-radiography and more particularly to a novel and improved X-ray spot filmer system of the type movably carried on the tower of a tiltable X-ray table for the taking of radiographs.
2. Prior Art
In X-ray examinations, it is now well known to provide a table body tiltably carried on a pedestal for supporting a patient in a selected horizontal, vertical, or inclined attitude during the taking of radiographs. An X-ray source is supported on a carriage in the table body and is movable longitudinally of the table. A tower assembly is coupled to the carriage and moves with the X-ray source along the table body. The tower assembly includes as up-standing tower structure for supporting X-ray imaging equipment at selected positions above the table top. An X-ray table of this type is described in the referenced Tiltable Table Patent.
If the physician wishes to take still pictures in the form of radiographs, an imaging device called a spot filmer is used. The spot filmer presents a sheet of film at an exposure station in the path of X-ray emission from the X-ray source carried in the table body. Spot filmers in present-day use include an automatic shutter mechanism and a carriage system for moving a sheet of film to different positions within the exposure station to selectively expose the entire film sheet or to sequentially expose selected portions of the film sheet. A spot filmer including a shutter mechanism of this type is described in the reference Shutter Control Patent.
Prior spot filmers utilize cassette-carried film. Each sheet of film is carried in a separate cassette. The spot filmer has a movable carriage which will receive and position one film cassette for exposure. When the exposure is complete, the exposed film cassette is removed from the spot filmer and a cassette containing an unexposed film sheet is inserted into the carriage for subsequent exposure.
The use of cassettes has a significant number of disadvantages, including:
a. The cassettes must be loaded individually in darkness, transported to the X-ray room where they will be exposed, and returned to a dark environment for unloading and developing. This individual handling of film sheets and relatively heavy cassettes is time consuming, cumbersome and expensive.
b. A large number of cassettes are required in hospitals and the like where a plurality of X-ray rooms are in use and each must be supplied with cassetted film.
c. The handling of cassettes during the taking of a series of radiographs is awkward and time consuming. Moreover, each of the films must be identified to assure that the radiographs are not confused with those of another patient.
d. The cassettes must be handled carefully to prevent the entrance of light and to prevent exposure by scatter radiation. When stored in an X-ray room, the cassettes require a radiation shielded enclosure.
e. Poor or unusable radiographs can result due to failure or weakening or improper positioning of the cassette springs which clamp the film sheet between a pair of intensifying screens. If the radiograph is unusable, it is necessary to return a patient to the radiograph table to repeat part or all of a radiograph film series.
In the past there have been proposals in various types of X-ray apparatus other than spot filmers for eliminating the use of cassettes in an effort to obviate cassette-related problems. Such proposals have called for the use of separate film storage magazines for holding exposed and unexposed film sheets. Unexposed film sheets are fed one at a time from an unexposed film magazine to an exposure station. Exposed film sheets are fed from the exposure station to an exposed film magazine.
The referenced "Cassetteless System Patent" describes a system where film sheets of different sizes are carried in different sized storage magazines and are selectively fed to an exposure station. After exposure, the film sheets are delivered to a common exposed film station. The described system utilizes a vacuum source to attain thorough, intimate contact between a film sheet and a pair of intensifier screens.
Spot filmer installations present a number of unique problems that militate against the use of prior cassetteless film handling systems in a spot filmer.
One such problem relates to counterbalancing. Since a spot filmer is movably supported on the movable tower of a tiltable X-ray table, its weight and the weight of its supporting tower must be carefully counterbalanced to permit the spot filmer and the tower to move easily regardless of the angle of inclination of the tiltable table top. The need for counterweighting necessitates that spot filmer weight be minimized. Moreover, as is explained in the referenced "Tiltable Table Patent", each kilogram of spot filmer weight requires not one but three kilograms of counterbalance weight. Hence, each kilogram of spot filmer weight imposes an added four kilogram load to the table. This added load necessitates the further strengthening of the table and as the table design is strengthened, still more weight is added.
In short, even a small amount of excessive spot filmer weight presents very significant design problems. Since prior cassetteless film systems have been designed for use in under-the-table installations and the like where the weight of the system has not posed a real problem, prior systems are typically too heavy for use in a spot filmer installation.
Still another problem that is peculiar to spot filmer film handling systems is that only a limited amount of space is available for the filmer. A modern X-ray room is equipped with a ceiling mounted X-ray source and other equipment that is used both with and in the vicinity of the X-ray table. In order to permit proper use of such equipment, the spot filmer must be of limited size and must be parkable at an out-of-the way position when not in use. Prior cassetteless film feed systems are not well adapted for spot filmer use inasmuch as they are too cumbersome and bulky.
Some prior film feeding systems have employed mechanical sensors for sensing the presence of a sheet of film at various positions along a film feed path. A problem with the use of such sensors has been that they drag on the film sheet leaving undersirable marks on the film and occasionally fouling the feeding of the film.